[emeryx09]

My textbook say that if 1-alkyne  is added to BH3, then a second addition of BH3 cannot be prevented, therefore diasmylborane should be used. I have trouble understanding why this is. Isn't hydroboration of 1-alkyne similar to hydroboration-oxidation of other alkynes, where it would lead to an enol, which would then form a ketone or an aldehyde, therefore leaving no double bonds which can attack another BH3? How can there be additional reactions with BH3?

[sjb]

My textbook say that if 1-alkyne  is added to BH3, then a second addition of BH3 cannot be prevented, therefore diasmylborane should be used. I have trouble understanding why this is. Isn't hydroboration of 1-alkyne similar to hydroboration-oxidation of other alkynes, where it would lead to an enol, which would then form a ketone or an aldehyde, therefore leaving no double bonds which can attack another BH3? How can there be additional reactions with BH3?

Do boranes react with carbonyls?

[emeryx09]

Do boranes react with carbonyls?

I don't quite understand...

[discodermolide]

Do boranes react with carbonyls?

I don't quite understand...

Does BH₃ react with aldehydes and ketones?

[orgopete]

This is confusing two different reactions. There aren't any carbonyl compounds until step two of the hydroboration (BH3)/oxidation (NaOH, H2O2) reaction. Your textbook is explaining why BH3 isn't used for terminal alkynes. BH3 reacts again with your alkenyl borane. Diasymylborane only has a single hydrogen and I presume less reactive.